be introduced because the supposedly unexposed population had some exposure to ETS, although they were classified as unexposed in the studies. Taking both types of errors into account produces an estimate of the excess lung cancer risk for nonsmokers married to smokers compared with completely unexposed individuals that is similar to the relative risk observed in the epidemiologic studies considered.
Since carcinogenic agents contained in ETS are inhaled by nonsmokers, in the absence of a threshold for carcinogenic effects, an increased risk of lung cancer due to ETS exposure is biologically plausible. Laboratory studies would be important in determining the concentrations of carcinogenic constituents of ETS present in typical daily environments. The use of biological markers in epidemiologic studies is recommended to more precisely quantify dose-response relationships between ETS exposure and lung cancer occurrence.
There have been few studies of risk for cancers other than lung in nonsmokers exposed to ETS. Some of the sites considered have been brain, hematopoetic, and all sites combined. The results of these studies have been inconsistent. Whether or not there is an association between ETS exposure and cancers of any site other than lung is an important topic for future epidemiologic inquiries.
Since active smoking has an adverse effect on cardiovascular disease morbidity and mortality, ETS exposure has also become suspect. Reports have noted an excess risk of cardiovascular disease in ETS-exposed nonsmokers; however, methodologic problems in the designs and analyses of these studies preclude any firm conclusions about the results. Studies reporting that ETS can precipitate the onset of angina pectoris among people who already have this condition are subject to the same precautionary note. Exposure to ETS produced no statistically significant effects on heart rate or blood pressure in school-aged children or healthy adult subjects, either during exercise or at rest. Data are not available as to possible adverse cardiovascular effects in susceptible populations, such as infants, elderly, or diseased individuals.